When transmitting content from a content provider to a subscriber in an encoded format, such as television programs streamed to a subscriber's set-top box via cable, the content has to be decoded at the set-top-box to be viewed by the subscriber.
As audio-video (AV) encoding standards evolve, compatibility with existing set-top box populations becomes problematic. For example, a content provider may wish to utilize the improved encoding standard of Motion Picture Expert Group 4 (MPEG4), while a portion of the set-top box population is only configured to decode content based on the earlier Motion Picture Expert Group 2 (MPEG2) standard.
One solution is to duplicate content on the network, broadcasting some content in more than one format. For example, content may be sent in both MPEG2 and MPEG4 formats. Perhaps MPEG4 encoding would be used for high definition (HD) content, while MPEG2 could be used for standard definition (SD) versions of the same content. However, this solution does not realize the full bandwidth benefits of the better encoding format; additionally some viewers will not be getting the benefit of the better encoding standard.
Another solution is to upgrade older set-top boxes with a transcoding unit. A transcoding unit can convert between encoding formats, it would output in a format compatible with the set-top box. For example, a transcoder could convert content from MPEG4 to MPEG2 encoding, so that the set-top box can decode from the MPEG2 standard. However, the transcoding process may introduce a loss of quality, it will also add delay, and a transcoding unit with current technology is expensive.